It's one thing to accuse a judge of bias. It's another to refer to a judge -- as Donald Trump did to the man presiding over the Trump University cases -- as a "Mexican." The judge, Gonzalo Curiel, happens to have been born in Indiana. But as far as Trump is concerned, this does not make him a Hoosier. Yet as Trump has doubled and tripled down on referring to the judge's ethnicity as grounds for bias, his lawyers have, at least so far, not filed a motion for recusal.

It's not hard to speculate why. Long after Donald Trump has moved on to a new battery lawyers for his next legal challenge, the ones who filed the recusal motion still have to practice before Judge Curiel. An attorney does his future clients a disservice by accusing the judge of bias solely, or even in part, based upon the parents' country of origin.

Yes, the judge belongs to San Diego La Raza Lawyers Association, which is a different group from the National Council of La Raza -- a group that advocates for, among another things, comprehensive immigration reform, aka amnesty. And the judge has made some rulings with which Trump disagrees. But that's what appellate courts are for.

That said, Trump should ask his critics why the silence over Judge and now-Justice Sonia Sotomayor's comments on the role of race and ethnicity in how judges reach decisions. In speeches before she became a Supreme Court justice, Sotomayor said, "I would hope that a wise Latina woman with the richness of her experiences would more often than not reach a better conclusion than a white male who hasn't lived that life." She also said, "Whether born from experience or inherent physiological or cultural differences ... our gender and national origins may and will (emphasis added) make a difference in our judging."

Trump is angry at a particular judge. But Sotomayor made a flat-out assertion that whites, blacks, Hispanics and women not only may, but will, make rulings according their sex, race and ethnicity -- whatever that means. How is this any less bigoted than Trump calling out Curiel because he's "Mexican"?

Suppose one of the white Baltimore cops accused of murdering Baltimore Freddie Gray filed a motion for recusal because the judge in charge of the case is black or because the black judge is a member of the NAACP? Courts have repeatedly ruled that a judge's race, gender or ethnicity does not constitute legal grounds for recusal. The California judge who ruled in favor of same-sex marriage was subject of a recusal motion because he is gay. It failed.

As to Trump, his tactic of legal belligerence seems to have served him well in the past. He has won or favorably settled most of the legal cases in which he was involved. He was a businessman. He's now a politician. As a businessman, the worst that can happen with a failed motion of judicial bias is that the lawyers make a bunch of money and you have a ticked-off judge. As a political candidate, the worst thing that can happen is that the lawyers make a bunch of money, you have a ticked-off judge and you have an indignant political constituency -- in this case, Hispanics -- whom Trump claims will vote for him.

Former Republican House Speaker Newt Gingrich, reportedly on the short list of VP candidates for Trump, called it "one of the worst mistakes Trump has made." Tennessee Sen. Bob Corker, also said to be under consideration for VP, likewise criticized Trump's reference to Judge Curiel's ethnic background. Not a single prominent Republican has defended Trump. Alabama's Sen. Jeff Sessions, a harsh critic of illegal immigration, has, so far, been silent.

An apology could be companied with a trademark attack on the media. After all, Trump could say, the media did not hyperventilate over then-presidential candidate Barack Obama's association with his bigoted pastor. Yet Trump could argue that when a Trump statement is perceived as bigoted, out come the axes. That is a legitimate double-standard argument to make, and Trump could have and should have made it. Instead he's off topic, wasting time and losing support.

Man up, Mr. Trump. Apologize. Then bring up Sotomayor. Ask why the double standard and the selective outrage. But going after Curiel is not the hill to die on.

At one of the Democratic debates, Bernie Sanders turned to Hillary Clinton and said: "The American people are sick and tired of hearing about your damn emails! ... Enough of the emails." Donald Trump said Sanders' taking this potent argument off the table suggested he did not really want to win. Trump insisted, "He's finished."